单项选择题

______,heat is produced.

A. Certain chemicals are mixed together
B. That certain ’chemicals are mixed together
C. Whenever certain chemicals are mixed together
D. The mixing together of certain chemicals

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单项选择题

By the first decade of the 21st century, international commercial air traffic is expected ______beyond today’s levels.

A. to have extended
B. to be extending
C. being extended
D. having been extended

单项选择题

Which statements is true as to the description of the NYMEX and IPE

A．They are both adopting open-outcry trading practice.
B．They are both making efforts to modernize the trading practice.
C．They are competing in the oil trading market.
D．They are competing to take the largest share in world’s commodity trad